Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $203.36   9.176%   $222.0203   $222.02   $222.00   $222.00  
  Purchase #2 $73.41   11.739%   $82.0276   $82.03   $82.05   $82.00  
  Purchase #3 $232.65   10.817%   $257.8158   $257.82   $257.80   $257.80  
  Purchase #4 $97.63   6.202%   $103.685   $103.69   $103.70   $103.70  
  Purchase #5 $237.62   8.292%   $257.3235   $257.32   $257.30   $257.30  
  Purchase #6 $101.94   13.398%   $115.5979   $115.60   $115.60   $115.60  
  Purchase #7 $167.93   9.733%   $184.2746   $184.27   $184.25   $184.30  
  7 purchase totals = $1,114.54       $1,222.7447   $1,222.75   $1,222.70   $1,222.70